Electrooptic devices are devices in which an applied electrical voltage produces a change in the optical properties of the device. Electrooptic devices are used for many applications such as variable transmission windows used for management of solar heat gain in buildings and variable transmission automotive mirrors. A specific type of an electrooptic device is an electrochromic device, i.e. a device that changes color in response to an applied voltage.
Electrochromic (EC) devices are a subset of electrooptic devices, provide reversible modulation of light, and are useful for several applications. Some of the applications are rearview mirrors for automobiles, trucks, buses, scooters and motorcycles; windows for automobiles, other transportation (including road, rail, water and air) and buildings; eyewear; and attenuation or modulation of artificial lighting, displays, and contrast enhancement filters (including variable transmission filters for helmet mounted displays). The only successful commercial application thus far has been for automotive rearview mirrors. High cost and lack of durability have limited commercial window applications of these EC devices.
The durability limitation of the EC devices arises in part due to the electrolytes and solvents used in the prior art. The typical high dielectric solvents used in present day devices may have one or more of the following drawbacks: high volatility, high moisture sensitivity, hydrophilicity, a narrow range of electrochemical stability, chemical reactivity, and susceptibility to light-induced degradation (typically from ultraviolet or UV light).
Recent progress with ionic liquids has shown that certain problems associated with conventional solvents may be overcome by the use of a variety of ionic liquid solvents that are organic solvents that are composed of ammonium cations and trifluoromethylsulfonyl-containing anions. In addition to overcoming the aforementioned problems, these solvents have a low flammability, thus making products incorporating them safer than products incorporating more conventional organic solvents.
The use of ionic liquids is described, for example, in PCT Patent Application WO 01/93363 to A. McEwen et al. entitled “Non-Flammable Electrolytes,” in Japanese Patent 98168028 to M. Watanabe et al. entitled “Room Temperature Molten Salts and Electrochemical Devices Using the Salts,” and in U.S. Pat. No. 6,365,301 to C. Michot et al. entitled “Materials Useful as Electrolytic Solutes,” which issued on Apr. 2, 2002, all of which are incorporated by reference herein. These papers and patents describe the use of ionic liquids in electrolytes, but fail to give specific details of electrolyte compositions and characteristics of the electrochromic devices made using ionic liquids.
One of the requirements of solvents for EC devices is that the other chemical components of the EC device are soluble and chemically stable with them. A limitation of the use of ionic liquids for electrooptic devices is that many of the known components of electrochromic devices have limited solubility in ionic liquids. Furthermore, the intrinsic limitations, e.g. electrochemical stability, of known electrochromic dyes and additives, are matched to conventional organic solvents, and therefore these dyes and other additives do not allow the full exploitation of the advantageous properties of the ionic liquids.
There remains a need for less expensive electrooptic devices with greater durability.
Therefore, an object of the present invention is to provide a relatively inexpensive, durable electrooptic device.
Another object of the present invention is to provide electrolyte solutions for electrooptic devices.
Yet another object of the present invention is to provide soluble dye compounds for use with ionic liquids for electrooptic devices.
Still another object of the present invention is to provide an electrooptic device with low leakage current.
Another object of the present invention is to provide an electrooptic device that utilizes low conductivity transparent conductors.
Yet another object of the present invention is to provide an electrooptic device suitable for use as a rear-view mirror for vehicles such as automobiles, trucks, buses, scooters, and motorcycles.
Still another object of the present invention is to provide electrooptic devices having fast kinetics to color and bleach.
Another object of the present invention is a method of providing removing impurities, especially colored impurities, from ionic liquid precursors.
Still another object of the present invention is a method for preparing ionic liquid using the conjugate acid of the anion of the ionic liquid.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.